1. Field of the Invention
2. Description of the Related Art
As off road biking has gained broader appeal, the demands that riders place on their bicycles have increased dramatically. Downhill, snow, and endurance races demand the increased traction and mobility of a two wheel drive bicycle system. Conventional bicycles are powered through a chain linking the pedal crankshaft to the rear wheel. Bicyclists are now facing many obstacles where having only rear wheel drive can lead to bicycle damage or personal injury. For professional riders, precious race time is lost avoiding obstacles such as logs, rocks, loose sand, mud, or ice. Traction and climbing ability are severely limited in extreme mountain conditions by only having the rear wheel provide power. In fact, biking professionals teach that only through learning to keep your weight on the rear wheel will beginners ever hope to improve their off-road skills. Accordingly, there is a need in the industry for a two wheeled drive bicycle which efficiently transfers power from the pedals to the front wheels, provides the rider with increased ability to safely negotiate rough terrain, and which does not detract from the aesthetic qualities and appearances of the bicycle structure itself.
The concept of a two wheel drive bicycle is not a new one. Several two wheel drive bicycle systems are patented at present using various combinations of chains, flexible cable shafts, and rocker arms mounted on the handlebars to transfer power either directly from the pedals to the front wheel or from the rear wheel to the front wheel. In general, two wheel drive bicycle systems fall into two categories: 1) permanent designs involving drive trains attached to the frame, and 2) retrofit kits which convert existing bicycles to two wheel drive. The main drawbacks to these systems are: 1) a modification to the standard bicycle in the form of a kit is expensive when considered as an addition to a bicycle purchase, 2) the low strength flexible shaft limits the allowable loading on the system, 3) the retro-fit kit requires considerable skill to attach and cannot be designed to optimally work with every frame design, and 4) the drive mechanisms are often large and openly exposed on the outside of the frame potentially creating additional hazards for the rider and detracting from the overall appearance of the bicycle.
U.S. Pat. No. 4,773,662 shows a bicycle with a front wheel driven by a chain connected to a handle-bar mounted hand pedaling system. The bicycle uses arm power to drive the front wheels and is adaptable to a conventional bicycle frame.
U.S. Pat. No. 5,542,689 shows a front wheel drive system for a bicycle which can be installed on a bicycle to drive the front wheel by rocking the handlebars back and forth. As with U.S. Pat. No. 4,773,662 mentioned previously, this bicycle attempts to harness the energy of the rider's arms as an additional power source for driving the bicycle. However, a drive mechanism requiring the use of the riders arms for more than steering, balance and control of the vehicle would likely create serious safety problems and interfere with the bicycle operation for both professional and recreational mountain bikers.
U.S. Pat. No. 5,052,705 describes a bicycle with power distribution from the rear wheel to the front wheel via a caliper and cable drive system. The drive system is activated by a caliper clamped on the rear wheel connected by a cable to a caliper on the front wheel. Inefficient power transfer to the front wheel due to slippage as well as torque loss in the cable would be a problem with this system.
U.S. Pat. No. 5,224,725 describes one permanent system that has been developed utilizing a series of chains and sprockets. This design involved many moving parts that would make the bicycle very awkward and difficult to maintain. The exposed chain that runs along the top tube would be hazardous to the rider and the front chain also would interfere with steering.
U.S. Pat. No. 5,324,057 describes a bicycle driven with a chain meshed with both the front and rear sprockets through a plurality of gears, pulleys and spring systems to power the front wheel.
Several two wheel drive bicycles demonstrate a front wheel driven by flexible cables or flexible cables in combination with chains. (See e.g., U.S. Pat. Nos. 5,332,244, 5,253,889, 5,158,314, 5,116,070, and 4,895,385) The systems, such as the bicycle produced by Turner Drive Systems of Rogers, Ark., target the market for a drive system which can be retrofit to any standard frame with modifications primarily to the gearing and chain attachments necessary to drive the front wheel.
As disclosed, U.S. Pat. No. 5,332,244 uses chain-sprocket arrangements, along with a flexible shaft to transmit some of the power from a rear gearbox to the front wheel. The retrofit system utilizes the inner most sprocket for the drive system, however the rider can use the other sprockets to shift gears normally. Deformation of the flexible cable, and corresponding loss of efficient power transfer from the rear wheel to the front wheel is a drawback of each of these systems when compared to the rigid shaft drive of the present invention.
U.S. Pat. No. 5,158,314 uses a complex mechanical system to power the front wheel from the powered rear wheel. A first traction chain coupled to the rear wheel and attached to the frame is connected to a series of rigid and flexible shafts which attach to a second traction chain which is mounted above the front wheel and powers the front wheel. U.S. Pat. Nos. 4,029,332 and 4,474,660 also describe two wheel drive bicycles with complex chain or belt drive and pulley systems. It is, therefore, the object of this invention to provide a two wheel drive bicycle which is powered by a rigid shaft drive system and, therefore, does not experience the loss of power due to slippage or elasticity associated with flexible shafts and other drive systems.
It is a further object of this invention to provide a two wheel drive bicycle wherein the rigid drive shaft system powers the front and rear wheels simultaneously in a ratio which enables safe and effective operation of the bicycle and provides immediate transfer of power from the pedals to the front wheel.
It is a further object of this invention to construct the bicycle frame in a manner that substantially encloses the shaft drive system and provides effective two wheel drive biking with no interference of rider motion, with normal braking and steering radius, and with minimal rider danger with respect to moving parts and obstruction of operation.
It is a further object of this invention to incorporate the two wheel drive technology into a shock-absorbing front fork to provide the rider with a smoother ride.
Other objects and advantages will be more fully apparent from the following disclosure and appended claims.